Abstract:

A carbon quantity detecting sensor for continuously detecting a carbon
quantity of measuring gases with increased precision using a simplifier
structure is disclosed. The sensor includes at least a proton conductive
body composed of a solid electrolyte body having a proton conductivity,
an electrode pair composed of a measuring electrode and a reference
electrode formed on the proton conductive body at opposing surfaces
thereof respectively, and a power source for applying at least one of a
given current or a given voltage across the electrode pair. The measuring
gases electrode is exposed to the measuring gases and the reference
electrode is isolated from the measuring gases. This enables the carbon
quantity of measuring gases to be detected with increased precision for a
long period of time without causing a carbon component to accumulate on a
surface of the measuring electrode due to an electrochemical reaction.

Claims:

1. A carbon quantity detecting sensor adapted to be installed in a flow
passage of measuring gases containing a carbon component for detecting a
carbon quantity of the measuring gases, the carbon quantity detecting
sensor comprising:at least a proton conductive body composed of a solid
electrolyte body having a proton conductivity, an electrode pair composed
of a measuring electrode and a reference electrode formed on the proton
conductive body at opposing surfaces thereof respectively; anda power
source for applying at least one of a given current or a given voltage
across the electrode pair; whereinthe measuring gases electrode is
exposed to the measuring gases and the reference electrode is isolated
from the measuring gases.

2. The carbon quantity detecting sensor according to claim 1, wherein:an
electric power is applied to the electrode pair from the power source to
allow the carbon component and water vapor present in the measuring gases
to be subjected to an electrochemical reaction on the measuring
electrode.

3. The carbon quantity detecting sensor according to claim 1, further
comprising:voltage potential measuring means for measuring a voltage
potential occurring across the electrode pair when applied thereto with a
given electric current.

4. The carbon quantity detecting sensor according to claim 1, further
comprising:current measuring means for measuring an electric current
flowing across the electrode pair when applied thereto with a given
voltage.

5. The carbon quantity detecting sensor according to claim 1, wherein:the
proton conductive body is made of pyrophosphate MP2O7 in which
tetravalent metallic cation or a tetravalent transition metal.

6. The carbon quantity detecting sensor according to claim 1, wherein:the
proton conductive body is made of ABO3 type transition metal oxide
with a perovskite structure having a principal component including at
least one of ZrO2 and CeO2 while containing at least one of
CaO, SrO and BaO.

7. The carbon quantity detecting sensor according to claim 1, wherein:the
proton conductive body is formed of a substrate body made of stabilized
zirconia having a surface a part of which is subjected to phosphate
treatment to be formed with a zirconium pyrophosphate layer.

9. The carbon quantity detecting sensor according to claim 1, further
comprising:a heating section for supplying the proton conductive body
with electric power to heat the same to a given temperature.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is based on Japanese Patent Application No.
2008-221599, filed on Aug. 29, 2008, the content of which is hereby
incorporated by reference.

BACKGROUND OF THE INVENTION

[0002]1. Technical Field of the Invention

[0003]The present invention relates to carbon quantity detecting sensors
and, more particularly, to a carbon quantity detecting sensor used for an
exhaust system of an automotive internal combustion engine to be suited
for detecting a quantity of carbon contained in measuring gases.

[0004]2. Description of the Related Art

[0005]In recent years, attempts have heretofore been made to use a common
rail type fuel injection system, a supercharge system, an oxidizing
catalyst, a diesel particulate filter (DPF), a selective catalyst
reduction (SCR) system and an exhaust recirculation (EGR) system in
combination. This achieves a reduction in environmental load substances
such as nitrogen oxides NOx, particulate materials PM and unburned
hydrocarbons, etc., contained in combustion exhausts emitted from a
diesel engine or a gasoline lean-burn engine or the like.

[0006]In general, the DPF, used in such a system, takes the form of a
honeycomb structure made of a raw material such as porous ceramics having
a large number of porous partition walls. The large number of porous
partition walls has an infinite number of fine pores that capture PM in
combustion exhausts. The PM accumulates in the fine pores, resulting in
the clogging of the fine pores with a resultant increase in pressure
loss. To overcome such deficiencies, attempts have heretofore been taken
to heat the honeycomb structure using a burner or a heater, etc. Another
attempt has been made to regenerate the DPF by performing a post
injection to inject a small quantity of fuel into the engine after
combustion explosion of the engine. This enables combustion exhausts with
high temperatures to be introduced into the DPF for heating up the DPF,
thereby combusting PM accumulated on the partition walls of the DPF for
removal.

[0007]In order to have further improved combusting efficiency of the
internal combustion engine, an OBD (On-board Diagnosis and an on-vehicle
failure diagnosing device) for determining a timing for such a DPF to be
regenerated and detecting degradation and damages to the DPF has been
desired. In addition, the internal combustion has been desired to have
detecting means that can continuously detect the amount of PM, contained
in combustion exhausts, with high accuracy in feedback control or the
like.

[0008]Patent Publication 1 (Japanese Patent Application Publication No.
2006-266961) discloses means for detecting a quantity of PM in combustion
exhausts. The detecting means includes a soot detecting sensor disposed
in a gas flow passage, through which gases containing soot pass, for
detecting soot contained in gases. The soot detecting sensor includes a
soot detecting electrode formed of an electrically conductive porous
substance, and at least one pair of electrically conductive electrodes
for measuring an electric current flowing through the soot detecting
electrode. With such a structure, measuring the electrical resistance
varying when soot is adhered onto the soot detecting electrode allows the
amount of soot to be detected.

[0009]Further, Patent Publication 2 (Japanese Patent Application
Publication No. 2006-322380) discloses a technology of providing an
oxidizing catalyst and a thermo couple on the DPF at an upstream side and
a downstream side thereof. This enables the detection of a difference
between an exothermic temperature, caused by oxidizing catalyst reaction
of combustion exhausts containing PM admitted to the DPF, and an
exothermic temperature resulting from an oxidizing catalyst reaction of
on-treated combustion exhausts passing through the DPF, thereby detecting
the amount of PM in combustion exhausts.

[0011]With the structure disclosed in Patent Publication 1, a method is
carried out for measuring the resistance value varying depending on the
amount of soot accumulated on the soot detecting electrode. This causes
the soot detecting electrode to have a risk of deterioration in detecting
sensitivity when soot is accumulated on the soot detecting electrode at a
level given value or more. In addition, there is another risk of a
difficulty encountered in making a distinction between a variation in
resistance is value of the soot detecting electrode, caused by a
variation in PM concentration of measuring gases, and a variation in
resistance value of the soot detecting electrode, caused by soot
accumulated on or remained on the soot detecting electrode with long-term
use.

[0012]With the method relied on a differential heat as disclosed in Patent
Publication 2, the differential heat is liable to an effect of a
variation in combustion exhaust temperatures caused by a variation in
operating condition of the internal combustion engine or an effect of a
variation in flow rate of measuring gases caused by the clogging of the
DPF. This causes a risk of a difficulty occurring in accurately detecting
the amount of PM in combustion exhaust.

[0013]Moreover, with the method of detecting the amount of PM in
combustion exhausts upon using optical means such as a semiconductor
laser or the like disclosed in Patent Publication 3, there is a risk of
causing a difficulty to arise for accurately performing the monitoring
due to a consequence of PM in combustion exhausts being accumulated on an
optical opening section for exchange of a laser light beam.

SUMMARY OF THE INVENTION

[0014]The present invention has been completed with a view to addressing
the above issue and has an object to provide a carbon quantity detecting
sensor having a simplified structure to continuously detect a quantity of
carbon contained in measuring gases with high precision.

[0015]To achieve the above object, a first aspect of the present invention
provides a carbon quantity detecting sensor adapted to be installed in a
flow passage of measuring gases containing a carbon component for
detecting a carbon quantity of the measuring gases. The carbon quantity
detecting sensor comprises at least a proton conductive body composed of
a solid electrolyte body having a proton conductivity, an electrode pair
composed of a measuring electrode and a reference electrode formed on the
proton conductive body at opposing surfaces thereof, respectively, and a
power source for applying at least one of a given current or a given
voltage across the electrode pair. The measuring gases electrode is
exposed to the measuring gases and the reference electrode is isolated
from the measuring gases.

[0016]With the carbon quantity detecting sensor of the first aspect of the
present invention, the electric power sources applies electric power
across the electrode pair to allow an electrochemical reaction to occur
on the measuring electrode to oxidize the carbon component in measuring
gases while making it possible to detect the carbon quantity. This
enables the realization of a carbon quantity detecting sensor that can
operate with increased reliability for a long-term period without causing
the carbon component, contained in measuring gases, to accumulate on the
measuring electrode.

[0017]With a second aspect of the present invention, electric power is
applied to the electrode pair from the power source to allow the carbon
component and water vapor present in the measuring gases to be subjected
to an electrochemical reaction on the measuring electrode.

[0018]With the carbon quantity detecting sensor of the second aspect of
the present invention, electrolysis of water vapor present in measuring
gases occurs to create active oxygen with extremely strong oxidative
power, which can oxidize the carbon component present in measuring gases.
This enables the realization of a carbon quantity detecting sensor that
can operate with increased reliability for a long period without causing
the carbon component, contained in measuring gases, to accumulate on the
measuring electrode.

[0019]More particularly, as a third aspect of the present invention, the
carbon quantity detecting sensor may preferably take a structure
including voltage potential measuring means for measuring a voltage
potential occurring across the electrode pair when applied thereto with a
given electric current.

[0020]With the carbon quantity detecting sensor of the third aspect of the
present invention, the voltage potential occurring across the electrode
pair can be monitored at all times. This enables the carbon component,
contained in measuring gases, to be accurately calculated depending on a
variation in voltage potential in terms of a given current value. This
enables the realization of a carbon quantity detecting sensor that can
operate with increased reliability for a long-term period without causing
the carbon component, contained in measuring gases, to accumulate on the
measuring electrode.

[0021]More particularly, as a fourth aspect of the present invention, the
carbon quantity detecting sensor may preferably take a structure
including current measuring means for measuring an electric current
flowing across the electrode pair when applied thereto with a given
voltage.

[0022]With the carbon quantity detecting sensor of the fourth aspect of
the present invention, the carbon component, contained in measuring
gases, can be calculated based on the detected current value while
causing a carbon component in measuring gases to be oxidized.

[0023]More particularly, like a fifth aspect of the present invention, the
proton conductive body may be preferably made of pyrophosphate
MP2O7 in which M is a tetravalent metallic cation or a
tetravalent transition metal.

[0024]With the fifth aspect of the present invention, the proton
conductive body exhibits proton conduction activity in a so-called
intermediate temperature range of not less than 100° C. and not
more than 500° C. Thus, no need arises for a heating section to be
provided for activating the proton conductive body to detect the carbon
quantity in high temperature fluid, serving as measuring gases, such as
combustion exhausts, etc., of the internal combustion engine. This allows
a carbon quantity detecting sensor to take a simplified structure with
increased reliability maintained for a long period without causing carbon
components, contained in measuring gases, to accumulate on the measuring
electrode.

[0025]More particularly, in a sixth aspect of the present invention, the
proton conductive body may preferably take a structure composed of the
ABO3 type transition metal oxide with a perovskite structure
including at least one of ZrO2 and CeO2 while containing at
least one of CaO, SrO and BaO.

[0026]With the carbon quantity detecting sensor of the sixth aspect of the
present invention, the proton conductive body exhibits proton activity in
a high temperature range of 500° C. or more and has high
mechanical strength. When applied to a diesel particulate filter (DPF)
for removing particulate matters contained in combustion exhausts emitted
from a diesel engine or the like, the carbon quantity detecting sensor
makes it possible to stably detect the carbon quantity even if exposed to
high temperature environments of 600° C. or more during
regeneration of DPF. This enables the realization of a carbon quantity
detecting sensor that can operate with increased reliability for a
long-term period without causing the carbon component, contained in
measuring gases, to accumulate on the measuring electrode.

[0027]More particularly, in a seventh aspect of the present invention, the
proton conductive body may be preferably formed of a substrate body made
of stabilized zirconia having a surface a part of which is subjected to
phosphate treatment to be formed with a zirconium pyrophosphate layer.

[0028]With the carbon quantity detecting sensor of the seventh aspect of
the present invention, it becomes possible to allow the proton conductive
body to obtain proton conductivity equivalent to that of the proton
conductive body made of pyrophosphate MP2O7 that is difficult
to be sintered. This enables the realization of a carbon quantity
detecting sensor that can operate with increased reliability for a
long-term period without causing the carbon component, contained in
measuring gases, to accumulate on the measuring electrode.

[0029]More particularly, like an eighth aspect of the present invention,
the measuring electrode and the reference electrode may preferably
include porous metallic electrodes containing at least one of gold Au,
platinum Pt, palladium Pd and silicon carbide SiC or cermet electrodes,
respectively.

[0030]With a ninth aspect of the present invention, the carbon quantity
detecting sensor may further preferably comprise a heating section for
supplying the proton conductive body with electric power to heat the same
to a given temperature.

[0031]With the carbon quantity detecting sensor of the ninth aspect of the
present invention, the proton conductive body can operate at a stabilized
temperature, thereby making it possible to detect the carbon quantity in
measuring gases with further increased precision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a typical schematic view showing an outline of a carbon
quantity detecting sensor of a first embodiment according to the present
invention.

[0033]FIG. 2 is a perspective exploded view showing an exemplary structure
of a carbon quantity detecting element for use in the carbon quantity
detecting sensor of the first embodiment shown FIG. 1.

[0034]FIGS. 3A to 3C are views showing test results of the carbon quantity
detecting sensor of the first embodiment shown FIG. 1, with FIG. 3A
representing a characteristic view showing variations in voltage
potential and CO2 concentration in terms of the presence of or
absence of carbon in measuring gases, FIG. 3B representing a typical view
showing an electrochemical reaction in the absence of carbon in measuring
gases and FIG. 3C representing a typical view showing an electrochemical
reaction in the presence of carbon in measuring gases.

[0035]FIGS. 4A and 4B are views illustrating detected results of the
carbon quantity detecting sensor of the first embodiment shown FIG. 1,
with FIG. 4A representing a characteristic view showing the
correlationship between a carbon concentration and an output voltage
potential when an applied electric current is applied, and FIG. 4B
representing a characteristic view showing the correlationship between an
applied current value and a detection limit.

[0036]FIG. 5 is a perspective exploded view showing an outline of a carbon
quantity detecting element of a second embodiment according to the
present invention.

[0037]FIG. 6 is a perspective exploded view showing an outline of a carbon
quantity detecting element of a third embodiment according to the present
invention.

[0038]FIG. 7 is a typical view in cross section showing an outline of a
carbon quantity detecting element of a fourth embodiment according to the
present invention.

[0039]FIG. 8 is a schematic typical view showing an outline of a
combustion exhaust purifying system using the carbon quantity detecting
element implementing the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

[0040]Now, a carbon quantity detecting element 10 of a first embodiment
according to the present invention and a carbon quantity detecting sensor
1, incorporating such a detecting element, will be described below with
reference to the accompanying drawings. However, the present invention is
construed not to be limited to such an embodiment described below and
technical concepts of the present invention may be implemented in
combination with other known technologies or other technologies having
functions equivalent to such known technologies.

[0041]The carbon quantity detecting sensor 1 of the present embodiment can
be utilized for various purposes. That is, the resulting detected value
is used for accurately for determining a timing at which a DPF (Diesel
Particulate Filter) is to be regenerated. Further, the resulting detected
value is used for detecting the occurrence of degradation in performance
of the DPF. Furthermore, the resulting detected value is used for OBD
(On-board failure self-diagnosing device) with which a breakage or the
like is determined. In addition, the resulting detected value is used for
performing rich spike control or the like in which fuel is injected to
combustion exhausts to achieve a reduction in PM and NOx.

[0042]As shown in FIG. 1, the carbon quantity detecting sensor 1 of the
first embodiment according to the present invention is fixedly mounted on
a measuring gas flow passage wall 2 of an internal combustion engine E.
This allows the carbon quantity detecting element 10 to have a measuring
section placed inside an exhaust gas flow passage 200 to detect
combustion exhausts, emitted from the internal combustion engine, as
measuring gases.

[0043]The carbon quantity detecting element 10 includes a proton
conductive body 100 formed in a plate-like configuration using a solid
electrolyte material with proton conductivity. The proton conductive body
100 has one surface, formed with a measuring electrode 110, and the other
surface formed with a reference electrode 120 placed in opposition to the
measuring electrode II 0, thereby forming an electrode pair.

[0044]The measuring electrode 110 is exposed to the flow of measuring
gases. However, the reference electrode 120 is covered with a proton
discharge channel-forming layer 131 in which a proton discharge channel
130 is defined in a structure isolated from measuring gases.

[0045]The measuring electrode 110 is connected to a positive electrode of
a DC power source 141 having a negative electrode connected to the
reference electrode 120. When a given DC voltage is applied across the
electrode pair composed of the measuring electrode 110 and the reference
electrode 120, an electric current flows across the electrode pair and
current detecting means 142 is connected the electrode pair to detect the
electric current flowing therebetween. In an alternative, voltage
detecting means 143 is connected between the electrode pair to detect a
voltage developed across the same. In addition, a computing device 140 is
connected to the current detecting means 142 and the voltage detecting
means 143 to calculate a carbon quantity in measuring gases based on a
detected result from the current detecting means 142 or the voltage
detecting means 143.

[0046]Combustion exhausts, emitted from the internal combustion engine E
and serving as measuring gases, contain granular particulate matter PM,
composed of soot and unburned hydrocarbon (HC), soluble organic fractions
(SOF) and sulfur oxides or the like, and, in addition thereto, water
vapor (H2O) in the form of a combustion product of fuel.

[0047]With a given DC voltage being applied across the electrode pair
comprised of the measuring electrode 110 and the reference electrode 120,
a reaction takes place in a manner as shown in a formula 1 described
below. In this moment, an electrochemical reaction of water vapor occurs
on of the measuring electrode 110 to generate active oxygen, which in
turn causes carbon in PM to combust for generating carbon dioxide.

C+2H2O→CO2+4H++4e.sup.- Formula 1

[0048]It turns out that during such a reaction, hydrogen ions move through
the proton conductive body 100 to permit an electric current I to flow
across the electrode pair or a voltage V to develop across the electrode
pair at rates correlated with a carbon quantity decomposed on the surface
of the measuring electrode 110.

[0049]Accordingly, using the current I flowing across the electrode pair
or the voltage V developed across the electrode pair, detected by the
current detecting means 142 or the voltage detecting means 143, results
in a capability of detecting an exact quantity of carbon decomposed on
the measuring electrode 110, i.e., a concentration of PM present in
measuring gases.

[0050]Further, hydrogen ions, generated on the electrochemical reaction of
water vapor, migrate through the proton conductive body 100 toward the
reference electrode 120 in a direction as indicated by an arrow A1 in
FIG. 1 for reaction with oxygen in atmospheric air admitted to the proton
discharge channel 130. This results in the formation of H2O, which
is discharged to the outside of the proton discharge channel 130.

[0051]With the carbon quantity detecting sensor 1 of the present
embodiment, carbon, contained in PM placed in contact with a surface of
the measuring electrode 110, is oxidized with active oxygen species O*
having an extremely strong oxidative power resulting from the
electrochemical reaction. Thus, no risk occurs for causing degradation in
sensor function due to the accumulation of PM on a sensor surface as
encountered in the related art PM sensor.

[0052]A more concrete structure of the carbon quantity detecting element
10 of the first embodiment according to the present invention and an
outline of a method of manufacturing the same will be described below
with reference to FIG. 2.

[0053]With the present embodiment, the proton conductive body 100 includes
a solid electrolyte preferably made of pyrophosphate MP2O7 (M
represents tetravalent cation) and, more particularly, made of stannum
pyrophosphate Sn0.9In0.1P2O7 to which indium was
doped.

[0054]Sn0.9In0.1P2O7 has a high proton defect
concentration and exhibits high proton conductivity in a so-called
intermediate temperature range at temperatures of 500° C. or less.
With the carbon quantity detecting element 10 placed in the combustion
exhaust passage 2 of the internal combustion engine E, the carbon
quantity detecting element 10 can be easily activated with combustion
exhaust temperatures. This makes it possible to obtain proton
conductivity with no need to provide specific means for heating the
proton conductive body 100. This results in a capability of achieving a
simplification in element.

[0055]Further, the proton conductive body 100 is formed in a substantially
plate-like configuration by a known ceramic forming method such as a
doctor-blade method and a press-forming method or the like.

[0056]The proton conductive body 100 has one surface formed with the
measuring electrode 110, a measuring electrode lead portion 11, a
measuring electrode terminal portion 112, and a reference electrode
terminal portion 122. The proton conductive body 100 has the other
surface formed with the reference electrode 120 and a reference electrode
lead portion 121. The reference electrode lead portion 121 and the
reference electrode terminal portion 122 are connected via a through-hole
electrode 123 extending through the proton conductive body 100 at one end
thereof.

[0057]Further, the measuring electrode 110 and the reference electrode 120
are composed of porous metal electrodes each containing one of gold Au,
platinum Pt, palladium Pd and silicon carbide SiC or cermet electrodes,
which can be formed by a known electrode forming method such as
thick-film printing, vapor deposition or plating or the like.

[0058]The measuring electrode lead portion 111, the measuring electrode
terminal portion 112, the reference electrode lead portion 121, the
reference electrode terminal portion 122 and the through-hole electrode
123 are made of materials containing metal with high electric
conductivity and formed by a known electrode forming method such as
thick-film printing, vapor deposition or plating or the like.

[0059]The proton discharge channel-forming layer 131 and a basic bottom
layer 132 are stacked on the other surface of the proton conductive body
100 in this order so as to face the reference electrode 120.

[0060]The proton discharge channel-forming layer 131 and the basic bottom
layer 132 are made of insulating ceramics such as, for instance, alumina
Al2O3 or the like and each formed in a substantially plate-like
configuration by the known ceramic forming method such as the
doctor-blade method and the press-forming method or the like.

[0061]The proton discharge channel-forming layer 131 includes a flat plate
a part of which is cut away to form the flat plate in a substantially
U-shape configuration with the proton discharge channel 130 being formed
in a central area of the flat plate.

[0062]The proton conductive body 100, formed with the measuring electrode
110 and the reference electrode 120, the proton discharge channel-forming
layer 131 and the basic bottom layer 132 are stacked on each other into a
unitary stack body, which is then subjected to a firing process. This
enables the formation of a unitized carbon quantity detecting element 10.

[0063]Further, while the present embodiment has been described with
reference to an example of using indium as dopant for the proton
conductive solid electrolyte, it can be speculated that even using
aluminum results in a consequence of obtaining a proton conductive solid
electrolyte similar to the proton conductive solid electrolyte using
indium.

[0064]Test results on the carbon quantity detecting sensor 1 of the first
embodiment according to the present invention is described below with
reference to FIG. 3.

[0065]In conducting tests, moistening helium containing 3% of water vapor
and 10% of oxygen was used as measuring-gas simulating combustion
exhausts of an internal combustion engine. Moistening helium was supplied
to the measuring electrode 110 at a given temperature (of, for instance,
200° C.) and the measuring electrode 110 was applied with electric
power from the DC power source 141 to allow a given current I (of, for
instance, 10 mV) to flow. Under such a condition, a test was conducted to
measure a voltage potential V occurring across the electrode pair and an
analysis was conducted using a gas chromatography to check components in
gaseous matter created on the measuring electrode 110.

[0066]Test pieces were prepared one for the measuring electrode 110 having
a surface coated with carbon and the other for the measuring electrode
110 having a surface uncoated with carbon and used to make a comparison
between differences in voltage potential V and generated gaseous matters
due to the presence of or absence of PM in measuring gases.

[0067]As shown in FIG. 3A, when no carbon was present in measuring gases,
the carbon quantity detecting sensor 1 of the first embodiment according
to the present invention detected the voltage potential V with a high
level wherein no carbon dioxide was detected on the measuring electrode
110 with only oxygen being detected. On the contrary, when carbon was
present in measuring gases, the carbon quantity detecting sensor 1 of the
first embodiment according to the present invention exhibited the voltage
potential V with a low value as indicated by a single-dotted line P1. It
was turned out that a significant amount of carbon dioxide for the coated
carbon and a small amount of oxygen were detected and carbon dioxide
carbon was completely oxidized. A broken line P2 represents a variation
in voltage potential detected by a carbon quantity detecting sensor of
the related art.

[0068]Under a situation where no carbon is present in measuring gases, it
is speculated, as shown in FIG. 3B, that an electrolysis reaction takes
place on the measuring electrode 110. This causes water vapor H2O to
be decomposed into oxygen ion O2- and hydrogen ion H+ with
oxygen ion O2 being immediately converted to an oxygen molecule
O2. The hydrogen ion H+ migrates through the proton conductive
body 100 to the reference electrode 120 to react with oxygen molecule
O2 present in the proton discharge channel 130 to form water which
is discharged.

[0069]Meanwhile, under a situation where carbon is present in measuring
gases, it is estimated that an electrolysis reaction takes place on the
measuring electrode 110 to cause water vapor H2O to be decomposed
into active oxygen species O* and hydrogen ion H+, as shown in FIG.
3C, wherein active oxygen species O* having a strong oxidative power,
oxidizes carbon coated on the surface of the measuring electrode 110 the
hydrogen ion H+ migrates through the proton conductive body 100 to
the reference electrode 120 to react with oxygen molecule O2 to form
water which is discharged.

[0070]Further, Raman spectroscopic analysis was conducted to directly
observe a process in which carbon was oxidized on the measuring electrode
10 and it was confirmed that permitting the flow of electric current I
resulted in the demonstration of absorption attributed to O22-
at about 900 cm-1. This suggests that a surface active oxygen
species occurring on the measuring electrode 110 is O22-.

[0071]When applying the electric current I with a given value across the
electrode pair, a remarkably increased variation takes place in the
voltage potential V detected in terms of the presence of or absence of
carbon in measuring gases. Therefore, using the carbon quantity detecting
sensor 1 of the present embodiment makes it possible to monitor a
variation in PM quantity in measuring gases upon measuring the voltage
potential.

[0072]Referring to FIGS. 4 to 4C, description is provided of the variation
in voltage potential V with variations in electric current I applied
across the electrode pair the carbon quantity detecting sensor 1 of the
present embodiment and a carbon quantity on the surface of the measuring
electrode 110.

[0073]As shown in FIG. 4A, it tuned out that there were one carbon
quantity region in which carbon was instantaneously oxidized in the
presence of the electric current I to cause the voltage potential to
increase to a high level (with high resistance) and the other carbon
quantity region in which it took much time for carbon to be oxidized
while sustaining a low voltage potential (with low resistance).

[0074]Further, it tuned out that the voltage potential V exhibited a high
voltage potential in the absence of carbon on the measuring electrode 110
and, as shown in FIG. 4B, there were different detecting limits depending
on the current I.

[0075]Accordingly, it is expected that a carbon quantity detecting sensor
can be realized with a capability of having further increased detecting
precision and response. This can be achieved upon correcting a detection
result of the carbon quantity detecting sensor 1 of the present
embodiment by adjusting the current I in accordance with the quantity of
PM present in combustion exhaust to obtain a corrected detection result.
This allows a combustion control of an internal combustion engine to be
executed with further increased precision upon using the corrected
detection result, while the corrected detection result can be utilized
for determining regenerative timing of a DPF.

Second Embodiment

[0076]FIG. 5 shows a carbon quantity detecting element 10A of a second
embodiment according to the present invention. The carbon quantity
detecting element 10A of the second embodiment differs from the carbon
quantity detecting element 10 of the first embodiment in features as
described below. That is, the proton conductive body 100 of the first
embodiment composed of the solid electrolyte of the MP2O7 type,
exhibiting the proton activity in the middle temperature range at
temperatures of 100° C. or more and 500° C. or less, is
replaced by a proton conductive body 100A of a structure employing
ABO3 type transition metal oxide with a perovskite structure
exhibiting a proton activity even in a high temperature range of
500° C. or more. In addition, the carbon quantity detecting
element 10A of the second embodiment further includes a heater section
for heating the proton conductive body 110A.

[0077]With the present embodiment, the proton conductive body 100A can be
formed of the ABO3 type transition metal oxide with the perovskite
structure that takes the form of a principal component of either
ZrO2 or CeO2 and includes either one of CaO, SrO and BaO. For
instance, SrZrO3 or the like may be preferably used and the proton
conductive body 100A is formed in a sheet-like configuration using such a
proton conductive body electrolyte material. Moreover, the proton
conductive body 100A can be formed by the known ceramic forming method
such as the doctor-blade method and the press-forming method, etc.

[0078]With the present embodiment, the carbon quantity detecting element
10A further includes heater section composed of a heating substrate 170.
The heating substrate 170 has one surface, facing the basic bottom layer
132 stacked on the proton conductive body 100A, which is formed with a
heating element 160 at one end portion of the heating substrate 170 and
heating lead portions 161a and 161b extending from terminal ends of the
heating element 160 in parallel to each other. The heating lead portions
161a and 161b end at the other end portion of the heating substrate 170
to be connected to ends of heating through-holes 163a and 163b, extending
through the heating substrate 170, whose other ends are electrically
connected to heating element terminals 62a and 62b formed on the surface
of the heating substrate 170. The substrate 170, formed in such a
structure, is stacked onto a lower surface of the proton conductive body
100A via the basic bottom layer 132, defining a part of the proton
discharge channel 130, resulting in a unitary structure. The unitary
structure is then subjected to firing, thereby forming the carbon
quantity detecting element 10A in a unitized structure.

[0079]With the present embodiment, the heating element 160 is connected to
an external power source via the heating element terminals 162a and 62b,
the heating through-holes 163a and 163b and the heating element lead
portions 161a and 161b. When applied with electric power, the heating
element 160 develops a heat at high temperatures thereby activating the
proton conductive body 100A. This enables the carbon quantity detecting
element 10A of the present embodiment to stably detect a carbon quantity
like the carbon quantity detecting element 10 of the first embodiment
even when using the proton conductive solid electrolyte of the high
temperature type.

Third Embodiment

[0080]A carbon quantity detecting element 10B of a third embodiment
according to the present invention is described with reference to FIG. 6.
The carbon quantity detecting element 10B of the third embodiment differs
from the carbon quantity detecting element 10 of the first embodiment or
the carbon quantity detecting element 10A of the second embodiment in
that a diffusion resistance forming layer 180 is stacked on the proton
conductive body 100 of the carbon quantity detecting element 10 of the
first embodiment or the proton conductive body 100A of the carbon
quantity detecting element 10A of the second embodiment such that as
bottom wall of the diffusion resistance forming layer 180 faces the
measuring electrode 110. The diffusion resistance forming layer 180 has
one end portion formed with a diffusion resistance layer 181 formed in
alignment with the measuring electrode 110 in a stack direction of carbon
quantity detecting element 10B. The diffusion resistance layer 180 serves
to restrict the flow of measuring gases admitted to the measuring
electrode 110.

[0081]With the present embodiment, the diffusion resistance forming layer
180 has the other end portion having one surface formed with a measuring
electrode portion 112b and a reference electrode terminal portion 122b in
areas longitudinally spaced from each other. With a view to applying
electric power to the measuring electrode 110, the diffusion resistance
forming layer 180 is formed with a through-hole electrode 113b for
electrical connection between the measuring electrode terminal portion
112b and the measuring electrode lead portion 111 connected to the
measuring electrode 110. Likewise, with a view to applying electric power
to the reference electrode 120, the diffusion resistance forming layer
180 and the proton conductive body 100A are formed with a through-hole
electrode 123b for electrical connection between the reference electrode
terminal portion 112b and the reference electrode lead portion 121
connected to the reference electrode 120.

[0082]The diffusion resistance layer 181 has an effect of restricting the
flow of measuring gases applied to the surface of the measuring electrode
110, thereby restricting the amount of PM oxidized on the measuring
electrode 110. This allows the carbon quantity detecting element 10B to
have a structure of a so-called limited current measuring type and it can
be expected to realize a carbon quantity detection with further increased
precision.

Fourth Embodiment

[0083]A carbon quantity detecting element 10C of a fourth embodiment
according to the present invention is described with reference to FIG. 7.
FIG. 7 is a cross sectional view showing the carbon quantity detecting
element 10C of the present embodiment placed in an area exposed to a
stream of measuring gases. With the carbon quantity detecting element 10
of the first embodiment, the proton conductive body 100 carries thereon
the electrode pair such that the electrodes sandwich the proton
conductive body 100. The proton conductive body electrolyte of the
MP2O7 is a material that is difficult to be sintered. This
results in a difficulty of obtaining a sintered body configured in a
plate-like shape like that shown with reference to the first embodiment,
causing a risk of and increase in production cost. To avoid such a
difficulty, the present embodiment contemplates the provision of the
carbon quantity detecting element 10C composed of a substrate body 190
composed of stabilized ZrO2, having excellent mechanical strength,
which is known as an oxygen conductive solid electrolyte. The substrate
body 190 has one surface a part of which is subjected to phosphate
treatment to be formed with a zirconium pyrophosphate layer 100c. The
zirconium pyrophosphate layer 100c has one surface on which a measuring
electrode 110c and a reference electrode 120c are formed in a spaced
relationship with only the measuring gases electrode 110c being exposed
to a stream of measuring gases MG. A proton discharge channel-forming
layer 131c is disposed on the surface of the zirconium pyrophosphate
layer 100c to cover the reference electrode 120c such that a proton
discharge channel 100c is defined.

[0084]With the carbon quantity detecting element 10C formed in such a
structure, the zirconium pyrophosphate layer 100c, formed over the
surface of the substrate body 190, exhibits a proton conductive body,
thereby making it possible to realize the carbon quantity detecting
element 10C with high precision like the carbon quantity detecting
element 10 of the first embodiment. In addition, the carbon quantity
detecting element 10C of the present embodiment may further include the
same heating structure as that of the second embodiment.

[0085]An outline of an exhaust gas purifying system having the carbon
quantity detecting sensor of the present invention applied to a diesel
engine E/G will be described below with reference to FIG. 8. The diesel
engine E/G is a direct-injection type diesel engine that includes a
high-pressure pump PMPFL arranged to accumulate high-pressure fuel
in a common rail R to allow an injector INJ to directly inject pressure
into a combustion chamber CC of the diesel engine E/G.

[0086]The diesel engine E/G has an exhaust manifold MHEX in which a
turbine TRB is mounted to be drive with a stream of exhaust gases. The
turbine TRB is connected to a supercharger TRBCGR, which is
rotatably driven compress a flow of intake air to be admitted to an inter
cooler CLRTRB by which the flow of intake air is cooled to allow a
stream of cooled intake air to be admitted to an intake manifold
MHIN. A part of combustion exhaust, discharged from the exhaust
manifold MHEX, is recirculated through a recirculation passage RC to
the intake manifold MHIN for improving a combusting efficiency.
Combustion exhaust, discharged from the exhaust manifold MHEX,
passes through an oxidizing catalyst DOC in which unburned hydrocarbon
HC, carbon monoxide CO and nitric monoxide NO are oxidized. Exhaust gas,
thus subjected to oxidizing treatment, is caused to further pass through
a diesel particulate filter DPF by which particular matters PM are
removed. In addition, combustion exhaust is delivered through a selective
catalyst reduction SCR, (not shown) to convert NOx into innoxious
compounds such as N2 and H2O in reduction to be exhausted to
the outside.

[0087]The diesel particulate filter DPF has an inlet and an outlet on
which the carbon detecting elements 10 of the present invention are
mounted. These carbon detecting elements 10 monitor the amount of PM
contained in combustion exhaust at all times, with detected outputs being
utilized for the DPF to be controllably regenerated and for OBD (On-board
failure self-diagnosing device).

[0088]The present invention is construed not to be limited to the
embodiments set forth above and may be implemented in various modes
without departing from the scope of the present invention.

[0089]For instance, the present embodiments have been described above with
reference to the example of the carbon quantity detecting sensor
installed on the internal combustion engine such as an automotive engine
or the like. However, the carbon quantity detecting sensor of the present
invention can be utilized for application to a large-scale plant of a
thermal power station or the like for detecting a quantity of carbon.

[0090]Furthermore, by controlling an electric current flowing across an
electrode pair in a pulsed current that can vary in a cyclic manner,
further increased detecting precision and improved response can be
expected.

[0091]In addition, while the present embodiments have been described above
with reference to an example of a so-called stack type sensing element
structure, an alternative may include a so-called cup type sensing
element structure having a proton conductive body formed in a bottomed
cylindrical configuration having an outer wall and an inner wall formed
with electrode layers, respectively.